Prior to the development of the present invention, in the retail sales industry it has become the normally accepted practice to utilize what is now commonly known in the packaging industry as "point-of-sale" packaging for the vast majority of packaged products being offered for sale in the various retail outlets This particular practice, as would generally be expected, has been instrumental in forcing the packaging industry to not only develop but also to implement both new equipment and operating practices which are capable of providing significant improvements in the overall quality of printing on the substrate material being used as the product packages In other words, the old style "brown box" is no longer acceptable in the packaging of products which are offered for sale in these retail sales outlets. Primarily as a result of this more demanding practice, flexographic printing equipment is generally in widespread use throughout such package printing industry. See, for example, the December, 1979, issue of Boxboard Containers, in which there was published an article entitled, "It's Time For A Change In Flexo". Flexographic printing technology, as pointed out in this article, was introduced for use in this area in the 1960's. It was then that convertors started to install the equipment which was necessary for them to initiate the use of the flexographic printing process. As soon as the equipment was installed, it became possible for the convertor to now print, slot, fold, glue, die-cut and bundle in a true production line-type operation with his new flexographic printing equipment.
In addition to all of the inherent advantages the convertor gained by such production line-type operation, this change in equipment to enable implementation of the flexographic printing process presented the convertor with the potential for expanded capabilities as well as other improvements in package printing at the same time. For some reason, however, these additional potential benefits were generally not immediately taken advantage of by the packaging convertor. This is evidenced by the fact that even with this new process and equipment, the majority of such convertors continued the practice of using the same old, outmoded printing plate systems which were being used prior to the introduction of the modern flexographic printing system in such packaging industry. The old printing plate system generally consisted of a relatively thick rubber plate which was secured to a fabric-like material In turn, this fabric-like material was then secured to a carrier material
In fact, it was not until the late 1970's and early 1980's that any significant change occurred in the printing plate system being used in this flexographic printing process. The use of a cellular polyurethane material as a backing material for flexible type printing plates was first introduced by the Rogers Corporation at that time. These flexible type printing plates are secured directly to one surface of such cellular polyurethane material in this system. In turn, such cellular polyurethane material is glued to the printing plate cylinder This glueing of such cellular polyurethane material to the printing plate cylinder is accomplished with either an adhesive film or with what is commonly known in the printing industry as "sticky back" tape Additionally, in some cases, such cellular polyurethane material is adhered to and supported on a polyester backing material, such as, mylar. In this case, such polyester backing material is then adhered to an outer working surface of such printing plate cylinder. Regardless, with or without such polyester backing material, the flexible printing plate is positioned on and adhered to the upper surface of such cellular polyurethane material in the Rogers Corporation system.
In view of the fact that this particular printing plate system is essentially adhered directly to the working surface of the printing plate cylinder with an adhesive material, it stands to reason that added care must be exercised in aligning and mounting such printing plate to the cellular polyurethane material as well as the printing plate system thereafter to such working surface of the printing plate cylinder so that proper alignment can be ensured This is particularly the case, for example, when a plurality of colors are required to be printed on the substrate material forming a product package. The time consumed to ensure, proper alignment of this printing plate system is costly to the convertor not only from the manpower expense but also from the loss in production time for the equipment. Obviously this added cost must be passed on to the consumer.
At the present time, it is also known in the prior art to use a substantially T-shaped member to both align and secure in place one end of a vinyl sheet having a printing plate mounted thereon to a bar-like member that is positioned on such working surface of the printing plate cylinder. Such bar-like member is disposed substantially parallel to the longitudinal axis of the printing plate cylinder. In this prior art arrangement, the back surface of the vinyl sheet is engaged directly with the working surface of such printing plate cylinder. In order to use this system, the T-shaped member is engaged with one end of the vinyl sheet and with the bar-like member disposed on such printing plate cylinder. The axially opposed other end of the vinyl sheet is normally secured to such working surface of the printing plate cylinder with either tape or with strap-like members This particular printing plate fastening system is known in the package printing industry as the Matthews Fast-Loc System and is in widespread use in such packaging printing industry. Use of such Matthews Fast-Loc System results in significantly reduced downtime being required on the printing equipment in order to achieve the necessary alignment of the printing plate on the working surface of such printing plate cylinder. This, therefore, enables an increase in the productivity of such printing arrangement to be achieved.
Even though each of the above-identified important technical advances in printing plates systems have generally enhanced the printing quality achieved on package-type substrate materials commonly used in the packaging industry, they, nevertheless, each have certain critical limitations associated with their use in this particular application. For example, even though the Rogers printing plate system does enable a generally poorer quality substrate material to be used as a package and is not as sensitive to other slight imperfections which may be present on the working surface of the printing plate cylinder, this printing plate system still requires a considerable amount of time be expended to set up in the printing arrangement so that the necessary alignment of the printing plate on the working surface of the printing plate cylinder is achieved. The Matthews' Fast-Loc printing plate system, on the other hand, can normally be set up rather quickly in the printing arrangement, however, this particular Fast-Loc System does require a somewhat higher quality substrate material to be used and will additionally be generally somewhat more sensitive to such imperfections which can be present on the working surface of such printing plate cylinders.
Another significant drawback common to both the Rogers, printing plate system and the Matthews' Fast-Loc system is that because the printing plate is mounted directly on the surface of the cellular polyurethane material and the vinyl sheet, respectively, the entire system must be removed in order to change printing plates.